Means for equalizing transmission over lines of different electrical charactrristics



G. K. THOMPSON.

MEANS FOR EQUALIZING TRANSMISSION OVER LINES 0F DIFFERENI' ELECTRICAL CHARACTERISTICS.

APPLICATION FILED OCT. 29. I9I8- I 1,415,907, Patented May 16, 1922.

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ATTORNEY IIQ G.K.TH0MPSON. v MEANS FOR EQUALIZING TRANSMISSION OVER LINES OF DIFFERENT ELECTRICAL CHARACTERISTICS APPLICATION FILED 0CT.29. I918.

1,415,907, Patented Ma 16,1922. I

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I Tim's-Inhabit. UPu'i'a Loss INVENTOR.

A TTORN UNITED STATES PATENT OFFICE.

GEORGE K. THOMPSON, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

MEANS .FOR EQUALIZING TRANSMISSION OVER LINES OiF DIFFERENT ELECTRICAL CHARACTERISTICS.

Specification of Letters Patent.

Application filed October 29, 1918. Serial No. 260,150.

.1 '0 all whom it may concern.

Be it known that I, Gnoncn K. THOMPSON, residing at Maplewood, in the county of lilssex and State of New Jersey, have invented certain Improvements in Means for Equalizing Transmission Over Lines of l)i'lierent Electrical Characteristics, of which the following is a specification.

This invention relates to telephone systoms and more particularly to the provision of n'ieaus whereby the electrical charactc'iristics of telephone lines may be equalized or rendered more uniform.

elocti cal characteristics varying with the length of the lines. These variations in the electrical. cl'iaracteristics of. different sub sci-fliers lines in a telephone system, intro- (li'ice a nu inhcr of variable effects in the telephone ervice to the different stations. F or emunnle, the different electrical characteristics result in different degrees or attenuation oi? the alternating telephone can rent passing over the subscribers lines, thus providing louder and more effective telephonic communication for subscribers connected by means oi short lines than for subscribors connected by means of long lines. Furthermore, in the common battery systems now so generally employed in all but the small communities, the resistance of the line causes a further effect on the trans n'iission, in that it reduces the amount of direct current which the transmitter receives from the central office battery and so renders it less ellicient in the generation of the alternatin telephone current. Likewise, in common batl ry systems employing electro-magnetic receiver --that is, receivers not incliulimg a permanent magnet but depending For their energization upon the current su1mly,this variation. in current supply introduces changes in the efliciency of the receiver. R is one of the objects of this "nation to reduce and. substantially elimiinle the ditlicnlties above mentioned, although other and further objects of the invention will be clear from the detailed deiwription hereinafter given.

'lhese objects are secured in accordance .l& the present invention by providing; a

phone lines have, in general, difl'erent cord circuit or other form of link connector employed for establishing intercommunication between dlfi'erent transmission lines,

with impedance or resistance elements, the

impedance of which'is automatically adjusted by means of marginal relays as the current flowing over the lines tends to increase or decrease. Preferably these impedance elements are normally short circuited so that for very long lines no ad-' ditional impedance is introduced, but when the cord circuit is associated with a shorter line the resultant increase in current flow energizes and locks up one or more marginal relays, thereby removing the short circuits from a sufficient number of impedance elements to reduce the current flow to the desired value. The impedance elements may, if desired, be locked in such manner as to impede both the flow of direct current and the flow of the alternatingsignaling currents generated at the subscribers"station.

As provided with filaments of tungsten, iron orother material having a positive temperature-resistance co-eliicient may be used as impedance elements, thereby producing further equalization between the steps introduced by the action of the marginal relays. .By employing ballast lamps which are normally short circuited or shunted, the additional loss due to the introduction of these lamps in circuit with long lines may he eliminated. Furthermore, thesubstantially uniform transmission obtained lay-this system may be made equal to or better than the average transmission heretofore obtained by the increased e'fliciency of the telephone transmitter which now becomes possible owing to the uniform current supply obtained. Moreover, the transmission may be increased by the employment of more eflicient electro magnetic receivers under more advantageous a further refinement, ballast lamps Patented May 16,1922.

ing drawings Figures 1, 2, 4, 5, 7 and 8 of which constitute circuit diagrams of siX different modifications of the invention, while Figs. 3 and 6 are curves illustrating certain features of the operation.

Referring-to Fig. 1, a cord circuit C is shown provided with plugs P and P, adapted to co-operate with the jacks of a plurality of subscribers lines, such as, for instance, the jacks J and J of subscribers lines Land L. The cord circuit is provided with-theusual source or direct current supply B and with the transformers or repeating coils 1 and 2 for transmitting alternatingtelephone currents coming in over one subscribers line to the other subscribers line. For the purpose of equalizing transmission marginal relays M, N, M and N are provided in the talking conductors of the cord circuit. Each of these marginal relays has a low resistance winding 3 normally included in the current supply circnit and a high resistance winding 4 which is normally short circuited over the back contactof the relay. In order to reduce transmission losses due to the windings of the'r'elays, the windings may be shunted by non-inductive resistances, if desired.

The operation of the circuit may now be understood by reference to the curves in Fig. 3. In this-figure, the curve D represents the variation of direct current flow with the variation in the impedance of subscribers lines. Itwill be noted that the current flow is less :Eor long lines and increases rather rapidly as the impedance of the line decreases; If the cord circuit of Fig. 1 is associated with a line-whose impedance lies between points 4 and 6, neither of the marginal relays M and N will be operated and the current supply will be somewhere'between .036 and105. When the cord circuit is associated with a line whose impedance lies'between points 2 and 4, the

current] flow will initially be between .05 and -.077'. This current flow is suflicient to energize the windings 3 of relay M which thereuponopens the short circuit normally existingalo'out its high resistance winding 4 so that the high resistance winding is now included 'in'the current supply path and the current at once falls as shown by the curve E','to a value lying between .036 and .05. This current flow through windings 3 and a in series is suflicient to retain the relay M energized. lVhen the cord circuit is associated with a linewhose impedance lies between points zero and 2, the initial cur rent flow will be between .077 and .178. This current flow is suflicient to energize both relays M and N through their low resistance windings, so that the short circuits about the high resistance windings are opened and the high resistance windings of both relays are included in circuit with the source of current supply and the current at once falls to a value lying between .030 and .05, as shown by the curve E.

The initial impulse of current is considerably higher than that, normally obtained but is not of sufiieiently long duration to cause any injury to the telephone instrument. The marginal action of the relays insures that the current supply will, alwztys be maintained within certain limits, regard less of the length of the line, and by providing a sufiicient number of relays and properly proportioning the resistances controlled by the relays, any desired current flow may be obtained. The relay W is so adjusted as to be somewhat slower in its action than the relay N to prevent the possibility of the relay M. ()1')0l'2ltl1lf f on a short line and thereby reducing the current sutiiciently to prevent the operation of the relay N. The operation of: the relays M and N is the same as relays M and N and need not be further described.

A slightly modified form of circuit is shown in Fig. 2 which diilers from that of Fig. l. in that the relays M, N. M and N are included bet-ween the battery source 13 and the windings of the induction coils l and 2, instead of being included directly in the talking circuit. a low impedance path for talking currents being provided through the condensers 5 and 0. In this case it is unnecessary to shunt the windings 3 and 4- of the relays by non-inductive resistances in order to reduce transmission losses. The operation of the circuit is similar to that of Fig. 1 and need not be "further described.

The arrangements shown in Figs. 1 and 2 are open to the objection that the two sides of the cord circuit are not balui'lccd when one of the relays is operated. This objection is overcome by means of the arrangement shown in Fig. 4-. in which relays M. N, M and N are each provided with tour windings, two low resistance windings 2") and 3 and two high resistance windings 4- and 4:, one low resistance winding being normally included in each conductor oi the cord circuit when the relay is not operatml and one low resistance winding and one high resistance winding being: included in each conductor of the cord circuit when the relay is in the operated position. By arranging the relays in this manner both the high and low resistance windings are divided and half of the resistance of each is included in each talking conductor so that a complete balance is obtained. is in the case oi Figs. 1 and 2, the relay M responds to a medium increase in current and both relays M and l to a 125 large increase in current. the relay N being slightly quicker in its action than the relay M. The circuit oi" Fig. 4- also dii'l ers from that of Fig. l in that the windings are not shunted by non-inductirc resistances. so that 1110 the impedances of the windings themselves serve to equalize the transmission of alternating telephone current as well as the supply of direct current. I

A. still further arrangement is illustrated in F 5. .ln this case the windings of relays are not utilized. to :furnish the inipedance elements for. the cord circuits but simple resistances 9, 11.0, ll and 12 and 9, 10, 11' and 12 are included in the two sides of the cord circuit in such a manner that a balance will always be obtained. Resistances 9 and 10 are normally shunted by the contacts of relay 7 while resistances 11 and 12 are normally shunted by relay 8. In a similar manner, the resistances 9, 10 and 11, 12, respectively, are controlled by the relays 8 and 7. Battery supply current is furnished through the windings of marginal relays M and N, for one end of the cord circuit, while the other end of the cord circuitis supplied through the windings of marginal relays M and N; Relay M coutrolsthe circuit of relay 7, while relay N controls the circuit of relay 8, the relay N being slightly quicker in its action than the relay In a similar manner, relays M and N control, the circuits of relays 7 and. 8. The resistances 9, 10, ll, 12, etc, are included in the cord circuit in such a manner as to impede both the flow of direct current and of alternating telephone current generated at the subscribers station.

The operationotl. the circuit of hi 5 may be understood from a consideration of the curves shown in Fig. 6, in which the curve F represents the variation in transmission with variation ()1? the im iiedance of subscribers lines which arenot provided with equah izing' means. Representing the transmission obtainr-id under the zero loop condition as zero and plotting the losses obtained over long loops in suitable transmission units it will be seen that the transn'iissiou, as indicated by the curve F, decreases with the increase in the impedance of the subsc ibers line. Where the cord circuit is provided with equalizing resistances, as shown in Fig. 5, however, both nnirggrinal relays M and N willv be operated upon loops from zero to loops having impedance of three-quarters of a unit. Relays 7 and 8 are energized over the trout contacts oi relays M and N and open the short circuits norn'ially existing about the resistances l). 10 and 1L l2, respectively, connected to the cord circuit of Fig. The transmission obtained over such loops employing instruments ott improved eillcioncy as shown by the curve (it will vary between one unit of gain and one unit ot less depending on the length of the loop.

For loops having; impedance from three quarters to one and one-half units, only the relay M will be operated, thcrelgiy rgiaine relay 7 to remove the short circuit rom re wimling s ot' marginal role.

sistances 9 and 10. The impedance of the circuit is now increased so that the transmission will again vary between one unit of gain and one unit of loss. For all loops having an in'ipedance greater than one and one halt units, neither relays M nor N receive sull icicnt current to one so their windings and, consecuiently, all of the resistances are short circuited. The transmission is, there tore, increased to a gain'oi? one unit tor a loop having impedance of one and onehali units, from which point the transmission falls oil to zero for lines having an impedance 0f two units and tlor lines having still greater im iwedance. the transmission further falls off, as shown by the curve G.

Instead of inserting; simple resistances in the two sides of the cord circuit, as in the case of llig. 5,. ballast lamps provided with tilaments of tungstein iron, or other material having a positive tempcratureresistance coetlicient may be employed as shown in ll In this figure, ballast lamps 1.3 and ll t. are included in the two sides or". the circuit for one end ot the cord and ballast lamps 13 and 14: are included in the two sides oi the circuit for the opposite end. The ballast lamps l3 and 1.4 are normally shunted. by the low resistance windings 3 and 3 ot the mar-- ginal relay M, so that tor long loops the nornial resistance of the lamps is eitectively eliminated. The relay M is also provided with high resistance windings 4t and 4-, which are normally short cirruited over the back: contacts oi said relay The arrangeineut oi the relay M with respect to the ballast lamps 1.3 and :41 is similar to that just describcnl. lVhen the cord circuit is used in connection with. a line oi. considerable le 5th the flow oi current over the line is too small to operate the relay hi: and, the resistaure ot the ballast lamps is practically slninted out of circuit. then the cord circuit is connected with a line somewhat shorter, so that the current flow tends. to be materially increased, the marginal relay M energized thereby opening}; the short circuit about its high resistance holdingwindings l and 4: so that the ballast lamps 13 and 14: are now sluintcd by paths of very high resistance and the effective resistance in both the talking: circuit and the current supply circuit becomes approximately that due to the ballastlamps themselves. The resist auce of these lamps increases with increase in the potential applied so that the current supplied to the sul )-station is .pt within reason able limits.

t-l slightly modified arrainremeut is shown in l lo. 8. in this case the current is supplied to one end of the cord circuit through the inu edancc due to the initial ener g sing M, and M the current lu ing sup 'ilied to the other end oi" the cord circuit through the similar windings conseipiently,

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liltl of marginal relays M and M Ballast lamps l3 and 14: and 13 and 14 are included in the battery supply leads but are normally short circuited over the back contacts of relays M M M and M respectively. When the cord circuit is used in connection with long lines, therefore, the impedance of the ballast lamps is ineffective since the ballast lamps are short circuited. Upon somewhat shorter lines, however, the increase in current supply is suflicient to energize the marginal relays M and M through their initial energizing windings, thereby opening the short circuits about ballast lamps 13 and 14 and closing locking circuits for the relays M and M through their locking windings. Both the battery supply and talking current must now pass through a circuit including the impedance of the ballast lamps and the resistance due to the two windings of the marginal relays in parallel. The tendency of the current to increase as the loops become shorter results in an increased resistance of the ballast lamps so that both the current supply and the transmission of alternating talking current are maintained within reasonable limits.

By means of the arrangements above disclosed, simple and effective means are provided for automatically equalizing the transmission over subscribers lines of different lengths. It will also be obvious that the general principles herein disclosed may be em bodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

What, is claimed is:

1. The combination of a plurality of transmission lines having different electrical characteristics, a link circuit for interconnecting said lines, impedances in said link circuit, means to substantially equalize the transmission over all of the lines with which the link circuit may be associated, said means comprising relays responsive in accordance with the electrical characteristics of different transmission lines, and means operated by said relays to vary the impedance of said link circuit in accordance with the electrical characteristics of different transmission lines to which the link circuit is connected.

2. The combination of a plurality of transmission lines having different electrical characteristics, a link circuit for interconnecting said lines, a source of direct current supply associated with said link circuit, means for substantially equalizing the transmission over all of the lines with which the link circuit may be associated, said means comprising impedances in said link circuit, relays operating in accordance with the electrical characteristics of different transmission lines, and means controlled by said relays to vary the impendances of said link circuit with respect to both direct and alter' nating currents in accordance with the elec trical characteristics of different transmission lines with which the link circuit is connected.

3. The combination of a plurality ol transmission lines having different electrical characteristics, a. link circuit for interconnecting said lines, impedances in said link circuit, and relays responsive to current flow over said lines to increase the impedance ol said link circuit as the current flow over the lines with which it is connected tends to increase so that the transmission will be substantially equalized over all of the lines with which the link circuit may be associated.

4. The combination of a plurality 0! transmission lines having different electrical characteristics, a link circuit for intercounecting said lines, a source of direct current supply associated with said link circuit, in]- pedances in said link circuit, and relays rcsponsive to current fiow over said lines from said source to increase the impedance of said link circuit as the current flow over the lines with which it is connected tends to increase so that the transmission will be substantially equalized over all of the lines with which the link circuit may be associated.

5. The combination of a pl rality of transmission lines having different electrical characteristics, a link circuit for intcrconnecting said lines, a source of current associated therewith, normally shunted impedance elements in said'link circuit and means responsive to an increase in the current flow from said source to remove the shunts from said impedance elements so that the trans mission will be substantially equalized over all of the lines with which the link circuit may b associated.

6. The combination of a plurality of transmission lines having dillercnt electrical characteristics, a link circuit for interconnecting said lines, a source of current associated therewith, normally shunted impedance elements in said link circuit and relays responsive to an increase in the current flow from said source to remove the shunts from said impedance elements so that the trans mission will be substantially equalized over all of the lines with which the link circuit may be associated.

7. The combination of a plurality of transmission lines having different electrical characteristics, a link circuit for interconnecting said lines, a source of current associated therewith, normally shunted ballast lamps in said link circuit, and means rcsponsive to an increase in the current flow from said source to remove the shunts from. said ballast lamps.

ll l) 8. The combination of a plurality of transmission lines having different electrical chara'.'teristics, a link circuit for interconnecting said lines, a source of current associated therewith, normally shunted ballast lamps in said link circuit, and relays responsive to an increase in the current flow from said source to remove the shunts from said ballast lamps.

9. In a telephone system, subscribers lines of: differing electrical characteristics, substation ior each line, a connecting means for establishing connections with said lines, and relay means in said connecting means responsive to variations in said electrical characteristics for rendering the transmis sion over the talkingcircuits of said lines substantially the same.

10. In a telephone system, subscribers lines of dififering electrical characteristics, substation sets for each line, a connecting means responsive to variations in said electrical characteristics for establishing connections with said lines, a source in said connecting means for supplying talking current for said lines, and relay means in said connecting means for rendering the flow of current from said source over said lines sub stantially the same.

11. In a telephone system, subscribers lines of: differing electrical characteristics a connecting means for establishing connections with said lines, and relay means in said connecting means responsive to variations in said electrical characteristics for rendering the transmission characteristics of said lines substantially the same.

12. In a telephone system, subscribers lines of differing electrical characteristics, a connecting circuit for establishing connections with said lines, a variable resistance included in series in the talking circuit oi: said connecting circuit, and means in said (I01l necting circuit responsive to variations in said electrical characteristics for controlling said variable resistance.

In testimony whereof, I have signed my name to this specification this 19th day of October, 1918.

GEORGE K. THOMPSON. 

